(1) Field of the Invention
This disclosure relates to a system for controlling a rotorcraft rotor.
(2) Description of Related Art
In general, control systems include control members presenting large lever arms and/or large amounts of travel between two physical abutments for the movement stroke of a control member. Specifically, in certain circumstances, the stroke of the free end of a conventional stick may be very large, e.g. more than several tens of centimeters.
Furthermore, with such conventional control members, in general use is made of only one piloting control law that is proportional in position. Under such circumstances, a position of the stick corresponds by way of example to an unvarying position of the rotor plane of the rotorcraft.
Such a mode of operation is implemented in particular for a mechanical control system in which the control member and the rotor are mechanically linked together by a plurality of cranks, rods, and swash plates.
Under such circumstances and by way of example, the large amount of travel of a stick makes it possible to cover the entire control range for the rotor and to pilot the rotorcraft with good sensitivity. For each movement of the stick, a proportional movement of the rotor takes place and the resulting response of the rotorcraft is controllable.
Furthermore, the large travel of the stick also enables a lever arm to be provided that is sufficient to counter large control forces.
Nevertheless, even with a large amount of travel, it can be found to be complex or indeed uncomfortable to keep the stick in a determined position. That is why, an assistance device, generally referred to as a “trim unit”, enables the pilot to place the stick in a certain position and allow means suitable for providing a compensation force to keep the stick in that position. In the language specific to piloting rotorcraft, this function may be referred to as “anchoring the stick” or indeed “zeroing the forces” (i.e. the forces on the stick).
Thus, in order to limit the forces on the control member, electrical or optical controls have subsequently been developed, in particular such as those described in Documents WO 01/87706 and U.S. 2004/0010354 for piloting the various movements of a rotorcraft rotor, and more generally by Document EP 2 226 531 for controlling the advance of a vehicle. A computer then receives information about the positioning of the stick and then controls a proportional servo-control. Such an electrical or optical control system is thus advantageous in that it enables the control member to be mechanically decoupled from the rotor that it controls.
Nevertheless, under such circumstances, in order to cover the full range of rotor movements, the travel of control members necessarily remains very large. In particular, it is equivalent to the travel of a mechanical control member. Such a travel amplitude thus constitutes a major constraint in the design of a cockpit and on the corresponding ergonomics. Thus, control member with large amounts of travel do not make it possible to guarantee good comfort in the cockpit.
Furthermore, the control law of the servo-control acting on the rotor when on the ground is unique and always consists in a direct law concerning position, i.e. each position of the control member corresponds to one position of the rotor. Unfortunately, such a control law is not appropriate for enabling control members of small travel to be used while also covering the entire range of movement of the rotor.